Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Goodwill from business combinations	$ 4,298,000	$ 110,447,000
Goodwill impairment	0	0	$ 0
Impairment of core deposits and intangibles	0	0	0
Amortization expense - other intangible assets	$ 11,300,000	9,200,000	9,900,000
Core deposits
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	11 years
Core deposits | State Bancorp, Inc.
Finite-Lived Intangible Assets [Line Items]
Core deposits intangibles from acquisition		19,300,000
Other
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	20 years
Intangible assets acquired	$ 660,000
Residential mortgage
Finite-Lived Intangible Assets [Line Items]
Aggregate principal balances of mortgage loans serviced	2,500,000,000	2,100,000,000	2,300,000,000
SBA Loans
Finite-Lived Intangible Assets [Line Items]
Total amount of loans serviced by bank	23,800,000	32,300,000	$ 26,900,000
Wealth Management
Finite-Lived Intangible Assets [Line Items]
Goodwill from business combinations	701,000	$ 0
Segments excluding Wealth Management
Finite-Lived Intangible Assets [Line Items]
Goodwill from business combinations	$ 3,600,000